If I have a naked pair which straddles two blocks (mini grids) but are in the same row or column can I delete relevant possibilities from both blocks or am I confined to the row or column in which the naked pairs are situated.

You can only make eliminated in the row or column shared by the two matching pairs. A more general way to say that is that you can only make eliminations from cells which "see" both cells, where "see" means share a row/column/block with each of the pair cells.